1. Technical Field
The invention relates to a power resistor module for electrical circuits. The power resistor module comprises at least one resistor element and at least one housing element, wherein the at least one resistor element is mounted at least section-wise between two electrically insulating, thermally conductive insulation elements in the housing element and the insulations elements at least section-wise abut against the at least one housing element. The invention further relates to a method for producing an electrical power resistor module for an electrical circuit, wherein at least one resistor element is compressed between two electrically insulating, thermally conductive insulation elements and at least one of the two insulation elements is pressed at least section-wise against a housing element.
2. Description of the Related Art
Power resistor modules are known as protection elements in electrical circuits. Power resistor modules are often referred to as braking resistors, discharging resistors or protective resistors, and electrical heating elements. They transform electric energy to heat.
For example, a braking resistor reduces excessive electric energy during the braking operation of an electric motor, whereby it must first of all be ensured that the power resistor module safely transforms high-voltage pulses into heat and dissipates the same into the ambiance.
In the prior art, resistance wires are frequently employed in power resistor modules to transform the electric energy into heat. A heating wire of a defined resistance alloy and dimensioned in correspondence with the required power is wound onto one or more insulation plate(s). The free ends of the wire of such a wire-wound heating element are each connected to an electrical cable entry by welding, crimping, or the like. To obtain an improved heat storage capacity and heat transfer to the ambient environment, the wire-wound heating element is electrically insulated and coupled in a heat-transferring manner with an appropriate heat sink, e.g., an aluminum profile body.
In the prior art, techniques are known which allow the coupling of a wire-wound heating element to an aluminum heat sink in an electrically insulated and heat-transferring manner. EP 1 681 906 A1 describes a method for producing a heating element. In the method defined therein, first a lining made of micanite is incorporated into a profile body, e.g., an extruded aluminum profile, which is closed all over. Then, the wire-wound heating element is pushed into the profile, with an air space being provided on all sides around the wire-wound heating element. For this reason, the wire-wound heating element has to be appropriately positioned and fixed for the next production steps. On the side opposite the cable outlet the profile is then closed with another micanite plate. Next, the air space is filled with magnesium oxide. The magnesium oxide thermally couples the wire-wound heating element to the profile body and stores heat for a delayed heat transfer and buffering, as well as for electrical insulation. To be able to reliably fulfill these purposes, the magnesium oxide has to be compressed using a vibration process. Then, additional magnesium oxide is filled in, after which the profile body can be closed. To this end, another micanite plate is inserted in the feed side or cable side. The cable side may include cable openings for passing therethrough the connecting leads for the wire-wound heating element. Finally, the front faces of the profile are sealed with a silicone sealing layer and then with a cement layer.
In EP 1 225 080 A2 a protection element for an electrical circuit is described. Here, a PTC resistor element is disposed in a layered structure between two sheets, which are likewise electrically insulated by a film and are adjacent to a heat sink.
Moreover, an electrical heating element is described in DE 85 03 272U1. The electrical heating element comprises a PTC heating element clamped in a flat tube between two insulated plates of pressed micanite. The use of a heating wire or a heating wire filament is, however, not mentioned in DE 85 03 272 U1.
The use of PTC heating elements is problematical because they are made of a ceramic material and can, therefore, easily break if they are not handled with utmost care. Moreover, PTC heating elements are more expensive than resistance wires of a like capacity.
The methods known in the prior art for thermally coupling a wire-wound heating element to a profile body in an electrically insulated, thermally conductive manner and for sealing the profile body are time-consuming and expensive. Many production steps are necessary to fill the profile body with the magnesium oxide, and the costs for the sealing substances employed and the expenditure of time needed for their drying are too high as well.